1. Field of the Invention
The present invention relates to a vertical deflection circuit for electron beams in pictures tubes of television receiver sets where a capacitor is charged by a constant current source for generating a control signal for a vertical deflection output stage, where the capacitor is periodically discharged after a vertical deflection period via an electronic switch and where a control signal for the electronic switch is derived from a counter circuit counting the lines of the television receiver picture.
2. Brief Description of the Background of the Invention Including Prior Art
A receiver circuit of the kind set forth above has been known from the integrated circuit TEA 2026 since about Mar. 1983. This circuit further comprises a first comparator circuit which is activated by the counter circuit and the comparator circuit compares the actual voltage at the capacitor with a reference voltage.
The saw-toothed voltage generated by an integrated circuit such as TEA 2026 includes a direct current component onto which the saw-tooth is superposed. A change of this direct current effects a vertical shifting of the picture. The amplitude of the saw-tooth voltage and thus the level of the picture can be changed in various ways. For example, the amplification of the current generator or the counter coupling of the output stage amplifier can be changed. The recited circuit, however, is associated with substantial disadvantages. For example, the picture size changes upon changing of the capacitor due to aging, temperature and the like. In addition, the level of the picture and the height of the picture are shifted during such changes of the capacitor. The setting of the amplitude and the adjusting of the position of the picture are not independent of each other. A change of the picture height, that is, of the amplitude of the deflection current, occurs in an unsymmetric way relative to the center of the picture. After an adjustment of the amplitude, there is therefore required a change of the position of the picture.